THE PHYSICAE EVOLUTION OF ACADIA. 
13 
The Silurian Phase. 
It will be understood from remarks in the preceding section 
that the Tower Ordovician is included in the Cambrian terrane; 
this is shown by the presence of the Tetragraptus fauna in 
southern New Brunswick, the Tremadoc in Cape Breton, and 
the Tlandeilo fauna in the northern part of New Brunswick. 
But what of the great Trenton and Hudson River faunas of the 
interior basin of North America and of the St. Lawrence valley? 
these are wanting in all Acadia and Maine , hence we assume 
that this region was above the sea during the long period of 
time marked by the deposition of these formations, and Acadia 
was again restored to the condition of dry land, which existed 
there at the opening of the Paselozic time. During this 
period, deep weathering and great erosion of its land surfaces 
took place; for while we find the succeeding terrane resting in 
some places on the upper beds of the Cambrian terrane, in others 
it rests on the Paradoxides beds, and elsewhere on the Huronian. 
We cannot doubt, therefore, that there was a great erosion of 
this part of the earth’s surface while Acadia thus remained above 
the sea in the later Ordovician age, and that deep weathering of 
the land surface then provided ample material for the building 
up of the succeeding terrane. 
As in the Cambrian time so also in the Silurian, one of the first 
steps in the process of formation building was the beginning 
of volcanic effusions with the piling up of diabases, felsites or 
ryolites and other igneous rocks, which, with the accompanying 
elastics, form the Bloomsbury formation in southern New Bruns- 
wick, and similar deposits in Northern Nova Scotia. These 
are about the horizon of the Medina sandstone of' New York. 
Resting upon these is a formation which, in most of the 
sections, is a fine dark shale, but which, at St. John, in its lower 
part, exhibits a thick, strongly cemented sandstone, with beds 
of such shale. In northern Nova Scotia this formation contains 
graptolites etc., of Clinton age; in southern New Brunswick it 
has Silurian fishes and Phyllopods, and at St. John, in this 
province, remains of land plants. 
The next formation is one of paler shale with more calcareous 
